Introduction

In 1953, the Exit Block Signal was introduced in the rulebook, after -
apparently - having been in use on the Copenhagen Suburban Railway for
some time. The purpose of the Exit Block Signal was to introduce a signal
to increase traffic capacity as it overcame some of the shortcomings of
the Exit Route Signal. 1953 was also the year when the Platform Exit Signal
was introduced.

Exit Block Signals have, like other signal types, undergone changes
during the time they have appeared in the Danish State Railway's rulebook.
The rules for the Exit Block Signals probably haven't changed much but
the actual use of the signals has.

The first Exit Block Signals were used where today's Platform Exit Signal
is the standard; as a combined departure and semi block signal in station
areas. This has been the most wide-spread use of Exit Block Signals
through time:

Most such applications originate from changes to existing interlockings
featuring Exit Route Signals and Exit Signal or Exit Signals only. Most
of these "older" style Exit Block Signals have now been replaced with newer
interlockings and the standard Platform Exit and Exit Signals, but a few
remain, primarily around the Copenhagen Suburban Railway where they originated.
However, some newer interlockings has brought this use of the Exit Block
Signal back

In "modern" times the Exit Block Signal has found a slightly different
walk of life as a signal helping break long stations into smaller blocks.
The Exit Block Signal is mostly being referred to by this "modern" function,
even though it is quite rare. The "modern" Exit Block Signal is a signal
that is inserted between Platform Exit Signals and the Exit Signal on long
stations to create an in-station block. Typically a long station has a
group of switches at the end of the "Platform Tracks" (see definition below)
and another group of switches at the end of the station, i.e. shortly before
the Exit Signal. The Exit Block Signal is placed before the last group
of switches, permitting a train to leave the platform tracks and proceed
to the outer switch group, thus creating the in-station block. The usually
fairly short block created between the Exit Block and the Exit Signals
is similar to the block between Platform Exit and Exit Signals on normal
length stations:

"Platform tracks" are station tracks that can hold a train being stopped
for operational purposes like exchange of passengers, a meet or to be overtaken.
A platform track need not actually have a platform to fit the definition.

Exit Block Signal Types

Exit Signals may be divided into two physical types, a 2-lamp and a 3-lamp
type as shown below, identical to the Exit Signal types:

The 2-lamp type is used on the Copenhagen Suburban Railway only. This
type was the first in service and descends from the single-arm semaphore
signal. The 3-lamp type is used on all other lines. There has previously
been a number of single-arm semaphore Exit Block Signals, also on non-suburban
lines, but these are all long out of service. Many of these installations
were only intermediate during resignaling.

Exit Block Signals may have a supplementary Route Destination
Indicator, a Reduced Speed Sign or a Numerical Speed Indicator. Currently
no Exit Block Signal with Numerical Speed Indicator is in service.

It is common on larger stations to find Exit Block Signals with a Dwarf
Signal at its foot. This is due to the fact that Exit Block Signals have
no significance to switching moves. The Dwarf Signal, on the other hand,
has no real significance to trains. Both signals operate in main routes.

Exit Block Signal Aspects and Indications

"Stop" (Danish: "Stop")

Stop.

X

X

X

X

"Stop and Proceed" (Danish: "Stop og Ryk Frem")

Stop. Then proceed cautiously at max. 40 km/h (25 mph). Route is not guaranteed
to be clear.

X

X

X

X

"Proceed" (Danish: "Kør")

Proceed to Exit Signal, which must be expected to show "Stop".

X

X

X

X

Proceed not exceeding prescribed speed

X

X

X

X

Permitted speed as shown on Speed board

X

Trains with active Cab Signal: Cab signal will govern

X

X

X

X

Train is routed towards the indicated destination

X

"Proceed Through" (Danish: "Kør Igennem")

Proceed, Exit Signal shows "Proceed" or better.

X

X

X

X

Proceed not exceeding prescribed speed

X

X

X

X

Permitted speed as shown on Speed board

X

Trains with active Cab Signal: Cab signal will govern

X

X

X

X

Train is routed towards the indicated destination

X

Exit Block Signal Usage

Converted Signals

The introduction of Exit Block Signals in 1953 was made possible by another
big improvement: The introduction of multiple aspect signaling. Until 1953,
only Distant Signals and Entry Signals had been permitted to advance signal
a Main Signal. Distant Signals were located on approach to Entry and (Automatic)
Block Signals while Exit Signals, if any, were advance signaled through
the "Proceed Through" aspect on the Entry Signal. Combined Main and Distant
signals never caught on in Denmark, probably due to the quite short distances
between Distant and Main Signals and thus the little need for them.

Adding Advance Signaling

On the Copenhagen Suburban Railway there were a few locations where signals
were spaced so closely that the Distant Signals had been omitted. This
of course led to restrictions in permitted speed and was generally not
desirable. The short-block/no advance signaling problem was an "after station
stop" problem, as the first block after a station had to be short to allow
close headways:

The introduction of multiple aspect signaling and the much closer headways
possible on the line also created a need for a more smooth station signaling.
The Danish State Railways has in newer times preferred to interface station
interlockings and line block systems by locating an Exit Signal on the
"boundary" between the two systems, a strategy known in a number of other
countries as well. With the Exit Signal outside the switch group following
the platform tracks, and another signal at the end of the platform tracks,
an in-station block could be created. Though the in-station block often
was rather short, it actually equaled many open-line blocks in length on
these densely trafficked lines:

Reducing headways

Quite a few Exit Block Signals originate from converted Exit Route Signals.
On normal stations it was possible with only very few changes to the interlocking
system to gain an extra (short) block in the station area, thus reducing
headways between trains.

The only technical difference between Exit Route and Exit Block Signals
is that the Exit Block Signals are constantly lit:

The real gain of converting Exit Route Signals to Exit Block Signals
is that the Exit Block Signal can allow a train to proceed from the platform
track to the Exit Signal even if the first block on the line is occupied.
This is not possible with Exit Route Signals since the "Route Set" indication
implies that the Exit Signal shows at least "Proceed":

Another gain of the replacement is the elimination of the - since 1953
- illogical use of steady green for a signal aspect advance signaling the
next signal to show at least "Proceed":

One can wonder why some Exit Route Signals were converted into Platform
Exit Signals and some were converted into Exit Block Signals. From a technical
point of view these conversions were almost identical and fairly simple.
The answer perhaps lies in the fact that the Platform Exit Signal with
its normal "No Passing" default indication wasn't really considered a Main
Signal, and thus not used for these conversions where headway reduction
was the goal. Later on, the Platfrom Exit Signal became the standard signal
for these applications, and the Exit Route to Exit Block Signal conversions
ceased.

Adding Automatic Block

It was previously quite common for Stations to have the Exit Signals located
at the end of the platform tracks, as an alternative to the Exit Route
Signal configuration shown above. When automatic block signaling was introduced
on the lines, it was preferred to have the station interlocking and the
line block system interface at an Exit Signal at the station limit as mentioned
above. This new Exit Signal was equivalent to the Exit Signal already extensively
used on stations with Exit Route Signals. The "old" Exit Signals were converted
to Exit Block Signals, thus avoiding any physical change and only requiring
a minimal change to the interlocking:

For incoming trains on an entry route there is no real difference:

For exiting trains the change comes in two steps:

The first step is that the new automatic line block system now permits
an exit route to be set even while the previous train is still in the first
block, as the governing signal will stay at "Stop" and switch to "Proceed"
as the train progresses. A manual block would typically prevent the exit
route from being set until the first block is clear. The earlier setting
of the exit route ensures that the signals clear as soon as possible thus
further reducing headways.

The second step is the addition of the extra signal, permitting the following
train to proceed to the new Exit Signal:

Example: Gentofte

Gentofte is a Station on the so called Northern Line between Copenhagen
and Hillerød, located just north of Hellerup. The current interlocking
dates back to 1957 when the station was resignaled together with neighboring
Station Lyngby. The Northern Line was at that time a mixture of electric
suburban trains and steam/diesel trains from the outer part of the line
which had not yet been electrified. Traffic was dense and this was reflected
in the new interlockings.

For some reason Gentofte got an electromechanical interlocking, probably
the last that was ever installed. Lyngby got a state-of-the-art relay interlocking
and signaling. It is likely that the interlocking in Gentofte was a re-use
of a fairly new interlocking from Fyn, where the whole line was being converted
into CTC.

The interesting thing about Gentofte is that while the station itself
is rather trivial, the platform track signals are not. In both through
tracks are Exit Block Signals to keep down the headway, as outlined above
. For some reason the siding got Exit Route Signals, maybe a leftover from
the re-used interlocking. These Exit Route Signals were probably the last
to be installed (original station layout shown):

The Exit Block Signal in track 2 (middle) is located shortly after the
end of the platform. This leaves the rest of track 2 as a safety overlap,
facilitating simultaneous entry of an opposing train into the siding:

This arrangement utilizes the whole length of the siding for a long
freight train to be overtaken while still keeping up the high traffic capacity
in the Through Tracks.

Gentofte had its siding removed in 1998 and is for all practical matters
abandoned as a station. Today the interlocking only remains to avoid having
to rebuild the aging line block. At some point in time the southern (leftmost)
tail track was removed. The corresponding Exit Route Signal was then converted
into an Exit Block Signal since an Exit Route Signal is not able to provide
the necessary flank protection for trains in track 2.

"Proceed" vs. "Proceed Through" in Secondary
Exit Routes

The basic distinction between "Proceed" and "Proceed Through" is for advance
signaling, as illustrated in the previous sections. In some cases, however,
"Proceed" is used instead of "Proceed Through" to indicate an exit route
that is in some ways inferior to the normally used exit routes from that
track. This is similar to how Platform Exit Signals handle inferior exit
routes. "Proceed" is used on these secondary routes regardless of the condition
of the signal ahead, as shown below:

When exiting towards Wrong Main track:

When crossing from one main track to another through a low-speed crossover
on a bidirectional line:

Where the characteristics of two exit routes differ significantly. This
use has become common since the introduction of ATC, since the ATC system
can only distinguish exit routes by reading the "Proceed"/"Proceed Through"
aspect (i.e. it cannot read Route or Speed Indicators which might in some
cases be a help):

Example: Long Station

The "modern" use of the Exit Block Signal is to sub-divide long stations.
The station below has a freight yard located outside the passenger platform
tracks. The usual structure of signals surrounding a switch group is maintained
around the outer switch group by a number of different signals, depending
on the operational requirements. Gray tracks are tracks without implemented
main routes:

Since freight trains depart from the yard, Platform Exit Signals are
installed here. On the right main from the passenger station is an Exit
Block Signal, permitting trains to leave the passenger tracks and pull
out to the outer switch group. The Exit Block Signal is not strictly necessary
from a headway point of wiev, since the distance to the Exit Signal is
relatively small, but an exit route directly to the Exit Signal would block
the switch group for other use. In this example, the Exit Block Signal
has been located sufficiently far from the switch group to keep the safety
overlap from blocking the switches, thus permitting other movements in
the switch group as well as permitting the train to continue in any direction:

The Platform Exit Signal remains at "Proceed" until the Exit Signal
clears:

For trains headed towards wrong main, the more restrictive signaling
on secondary exit routes comes into action. The Exit Block Signal only
shows "Proceed" even though the Wrong Main Exit Signal also shows "Proceed":

Alternatively it is possible to by-pass the Exit Block Signal if so
desired:

Peculiarities

The most peculiar about Exit Block Signals today is that there are no real
peculiarities....